JP5862203B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Some multicolor image forming apparatuses such as color laser printers are provided with the same number of chargers as the number of colors of each developer (yellow, magenta, cyan, black). In Patent Document 1 below, in this type of image forming apparatus, by sharing a high voltage power supply unit (voltage application circuit) that applies a high voltage to each charger, the number of parts is reduced and the apparatus is downsized. Have been disclosed.

JP-A-3-142484

When the high-voltage power supply unit is shared as described above, the voltage level applied to each charger cannot be individually adjusted. On the other hand, the wire dirt provided in each charger is not necessarily uniform. For this reason, when the voltage power supply unit is shared, the discharge amount of each charger may vary and abnormal discharge may occur.
The present invention has been completed based on the above circumstances, and an object thereof is to suppress abnormal discharge in an image forming apparatus having a common voltage application circuit.

An image forming apparatus disclosed in this specification includes a photoconductor, a plurality of scorotron chargers that charge the photoconductor, and each of the scorotron chargers connected in common, and charging that applies a voltage to each of the scorotron chargers. A voltage application circuit; each wire provided in each scorotron charger; each grid electrode provided in each scorotron charger; a current detection unit that detects a grid current flowing through each grid electrode; and Grid current for constant current control of the maximum grid current so that the maximum grid current having the maximum value among the grid currents flowing through the grid electrodes becomes a first threshold value equal to or greater than a reference value by adjusting the output of the voltage application circuit. And a control unit.
The first threshold means a threshold corresponding to the upper limit of the grid current, and an upper limit value of the grid current or a numerical value having a margin with respect to the upper limit value can be used.

  In the image forming apparatus disclosed in this specification, since the maximum grid current is controlled at a constant current to the first threshold value, an abnormal discharge of the charger, that is, a large discharge current from the charger wire to the photoreceptor is prevented. it can. Therefore, it is possible to prevent deterioration of the photoreceptor.

In the image forming apparatus, the following is preferable.
The grid current control unit performs constant current control on the minimum grid current so that a minimum grid current having a minimum value among the grid currents flowing through the grid electrodes at the start of control becomes the reference value. After the maximum grid current reaches the first threshold, constant current control is performed on the maximum grid current so that the maximum grid current becomes the first threshold.

A first notifying unit for notifying an error of the scorotron charger in which the grid current flowing through the grid electrode is equal to or smaller than a second threshold value smaller than the reference value during the constant current control of the maximum grid current; The second threshold value means a threshold value corresponding to the lower limit of the grid current, and a lower limit value of the grid current or a numerical value with a margin for the lower limit value can be used.

Each developing device that supplies a developer of each color to each of the plurality of photoconductors provided, a developing voltage application circuit that applies a developing voltage to each developing device, and a developing voltage of each developing device A development voltage controller that controls the development voltage application circuit so as to achieve a target value;
The developing voltage controller is configured to supply the developer to the photoconductor facing the scorotron charger in which the grid current flowing through the grid electrode is lower than a reference value during constant current control of the maximum grid current. Then, control for lowering the target value of the development voltage is performed.

A second notification unit for reporting an error in the scorotron charger for charging the photosensitive member supplied with the developer from the developer whose applied developing voltage has become lower than a lower limit;

  According to the image forming apparatus of the present invention, abnormal discharge can be suppressed in an image forming apparatus having a common voltage application circuit.

1 is a schematic cross-sectional view illustrating an internal configuration of a printer according to a first embodiment of the invention. Diagram showing the structure of the process unit Diagram showing the structure of the charger Block diagram showing the electrical configuration of the high-voltage power supply Diagram showing grid current control flow Block diagram showing the electrical configuration of the printer Graph showing the relationship between the number of printed sheets and the charging voltage Graph showing the relationship between the number of printed pages and grid current of each channel Graph showing the relationship between the number of prints and the load on the charger The figure which shows the grid current control flow of Embodiment 2. Graph showing the relationship between the number of printed sheets and the target value of development voltage Diagram showing another flow of grid current control Diagram showing another configuration example of the printer

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS.

1. Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the internal configuration of a printer 1 according to this embodiment (an example of an “image forming apparatus” according to the present invention). In the following description, when distinguishing each component for each color, subscripts of B (black), Y (yellow), M (magenta), and C (cyan) are added to the reference numerals of the respective parts and are not distinguished. In this case, the subscript is omitted.

  The printer 1 includes a paper feeding unit 3, an image forming unit 5, a transport mechanism 7, a fixing unit 9, a belt cleaning mechanism 20, and a high voltage power supply device 100. The paper feed unit 3 is provided at the lowermost part of the printer 1 and includes a tray 17 that accommodates sheets (paper, OHP sheets, and the like) 15 and a pickup roller 19. The sheets 15 accommodated in the tray 17 are taken out one by one by a pickup roller 19 and are sent to the transport mechanism 7 via the transport roller 11 and the registration roller 12.

  The transport mechanism 7 transports the sheet 15 and is installed in the printer 1 above the paper feed unit 3. The transport mechanism 7 includes a driving roller 31, a driven roller 32, and a belt 34, and the belt 34 is bridged between the driving roller 31 and the driven roller 32. When the drive roller 31 rotates, the surface of the belt 34 facing the photosensitive drums 41B, 41Y, 41M, and 41C moves from the right direction to the left direction in FIG. As a result, the sheet 15 sent from the registration roller 12 is conveyed below the image forming unit 5.

  The belt 34 is provided with four transfer rollers 33B, 33Y, 33M, and 33C corresponding to the four photosensitive drums 41B, 41Y, 41M, and 41C. Each transfer roller 33 is disposed at a position facing each of the photosensitive drums 41B, 41Y, 41M, and 41C with the belt 34 interposed therebetween.

  The image forming unit 5 includes four process units 40B, 40Y, 40M, and 40C and four exposure apparatuses 49B, 49Y, 49M, and 49C. The process units 40B, 40Y, 40M, and 40C are arranged in a line in the conveyance direction of the sheet 15 (the left-right direction in FIG. 1).

  Each process unit 40 has the same structure, and each color photosensitive drum (an example of the “photoreceptor” in the present invention) 41B, 41Y, 41M, 41C, and each color toner as a developer (for example, a positively charged non-magnetic single component) The structure includes a toner case 43 containing toner, a developing roller (an example of the “developing device” of the present invention) 45, and chargers 50 </ b> B, 50 </ b> Y, 50 </ b> M, and 50 </ b> C.

  Each of the photosensitive drums 41 </ b> B, 41 </ b> Y, 41 </ b> M, and 41 </ b> C has a positively chargeable photosensitive layer formed on an aluminum substrate, for example, and the aluminum substrate is grounded to the ground of the printer 1. .

  The developing roller 45 is disposed below the toner case 43 so as to face the supply roller 46, and when the toner passes between the two, the toner is triboelectrically charged by friction caused by rotation to form a uniform thin layer. It fulfills the function of supplying the photosensitive drums 41B, 41Y, 41M and 41C.

  Each of the chargers 50B, 50Y, 50M, and 50C is a scorotron charger, and includes a shield case 51, wires 53, and a metal grid electrode 55 as shown in FIGS. The shield case 51 has a rectangular tube shape that is long in the direction of the rotation axis of the photosensitive drum 41. In the shield case 51, the surface facing the photosensitive drum 41 is opened as a discharge port 52.

  The wire 53 is made of, for example, a tungsten wire. The wire 53 is stretched in the direction of the rotation axis (left and right in FIG. 3) in the shield case 51, and a high voltage is applied by a charging voltage application circuit 200 described later. The wire 53 causes corona discharge in the shield case 51 by applying a high voltage. Then, ions generated by corona discharge flow from the discharge port 52 to the photosensitive drum 41 as a discharge current, so that the surface of the photosensitive drum 41 is uniformly charged to a positive polarity.

  A plate-like grid electrode 55 having slits and through holes is attached to the discharge port 52 of the shield case 51. By applying a voltage to the grid electrode 55 and controlling the applied voltage, the charging voltage of the photosensitive drum 41 can be controlled.

  The chargers 50B, 50Y, 50M, and 50C are provided with a wire cleaner 57. The wire cleaner 57 is slidable along the wire 53. The wire 53 can be removed by the operator reciprocating the wire cleaner 57 along the wire 53.

  Each exposure device 49B, 49Y, 49M, 49C has, for example, a plurality of light emitting elements (for example, LEDs and laser light sources) arranged in a line along the rotation axis direction of the photosensitive drums 41B, 41Y, 41M, 41C. By emitting light in accordance with image data input from the outside, it functions to form an electrostatic latent image on the surface of each photosensitive drum 41B, 41Y, 41M, 41C.

  A series of image forming processes by the laser printer 1 configured as described above will be briefly described. When the printer 1 receives the print data D (see FIG. 6), the printer 1 starts the printing process. As a result, the surfaces of the photosensitive drums 41B, 41Y, 41M, and 41C are uniformly positively charged by the chargers 50B, 50Y, 50M, and 50C as they rotate. Then, laser light is irradiated from each exposure device 49 toward each photosensitive drum 41B, 41Y, 41M, and 41C. As a result, a predetermined electrostatic latent image corresponding to the print data is formed on the surface of each photosensitive drum 41B, 41Y, 41M, 41C, that is, the positively charged photosensitive drums 41B, 41Y, 41M, 41C. Of the surface, the potential of the portion irradiated with the laser light decreases.

  Next, the rotation of the developing roller 45 causes the toner carried on the developing roller 45 and positively charged to be supplied to the electrostatic latent images formed on the surfaces of the photosensitive drums 41B, 41Y, 41M, and 41C. . As a result, the electrostatic latent images on the photosensitive drums 41B, 41Y, 41M, and 41C are visualized, and toner images by reversal development are carried on the surfaces of the photosensitive drums 41B, 41Y, 41M, and 41C.

  Further, in parallel with the processing for forming the toner image described above, processing for conveying the sheet 15 is performed. That is, as the pickup roller 19 rotates, the sheets 15 are sent one by one from the tray 17 to the paper transport path Y. The sheet 15 sent to the paper transport path Y is transported to a transfer position (a point where the photosensitive drum 41 and the transfer roller 33 are in contact) by the transport roller 11 and the belt 34.

  Then, when passing through this transfer position, each color toner image (developer image) carried on the surface of each photosensitive drum 41 is sequentially applied to the surface of the sheet 15 by the transfer bias applied to each transfer roller 33. Superimposed transfer. Thus, a color toner image (developer image) is formed on the sheet 15. Thereafter, when the toner image passes through the fixing unit 9 provided behind the belt 34, the transferred toner image (developer image) is thermally fixed, and the sheet 15 is discharged onto the discharge tray 60.

2. Configuration of High Voltage Power Supply Device 100 As shown in FIG. 4, the high voltage power supply device 100 includes a charging voltage application circuit 200, a PWM signal smoothing circuit 210, a charging voltage detection circuit 240, constant voltage circuits 250B, 250Y, 250M, 250C, grid current. Detection units 260B, 260Y, 260M, and 260C, development voltage application circuits 270B, 270Y, 270M, and 270C, development voltage detection circuits 280B, 280Y, 280M, and 280C, and a control device 110 are provided.

  The PWM signal smoothing circuit 210 is an integrating circuit composed of a resistor and a capacitor. The PWM signal smoothing circuit 210 smoothes the PWM signal S0 output from the PWM port P0 of the control device 110 and outputs the transistor Tr1 provided in the charging voltage applying circuit 200. Output to the base.

  The charging voltage application circuit 200 functions to generate a high voltage of about 6 kV to 8 kV from an input voltage of DC 24 V and apply it to each charger 50. In the present embodiment, a self-excited flyback converter (RCC) is used for the charging voltage application circuit 200. The charging voltage application circuit 200 includes a transformer 201, a smoothing circuit 203 provided on the secondary side of the transformer, A transistor Tr1 provided on the primary side of the transformer 201 and a feedback coil 205 are provided.

  The transistor TR1 switches the transformer 201. The emitter is connected to the ground, and the collector is connected to the primary winding of the transformer 201. A PWM signal smoothing circuit 210 is connected to the base via a feedback coil 205.

  Wires 53 of the respective chargers 50B, 50Y, 50M, and 50C are commonly connected to the output line Lo of the charging voltage application circuit 200. Thereby, the output voltage Vo of the charging voltage application circuit 200 is applied to the wire 53 of each charger 50B, 50Y, 50M, 50C.

  The charging voltage detection circuit 240 detects the output voltage Vo of the charging voltage application circuit 200, and includes an auxiliary winding 241 provided on the primary side of the transformer 201 and an integration circuit 243 including a resistor and a capacitor. Yes. The charging voltage detection circuit 240 is connected to the A / D port A0 of the control device 110, and is configured such that data of the output voltage Vo of the charging voltage application circuit 200 is taken into the control device 110.

  As shown in FIG. 4, in this embodiment, connection lines L1 to L4 are provided for the respective chargers 50B, 50Y, 50M, and 50C, and the grids of the respective chargers 50B, 50Y, 50M, and 50C are provided. The electrode 55 is connected to the ground through the connection lines L1 to L4. A constant voltage circuit 250 and a grid current detection unit 260 are provided on each connection line L1 to L4.

  The constant voltage circuits 250B, 250Y, 250M, and 250C are composed of three Zener diodes connected in series. The voltage values of the grid electrodes 55 of the respective chargers 50B, 50Y, 50M, and 50C are determined for each Zener diode. The voltage is made constant to a voltage value (for example, 250 V × 3) obtained by triple the breakdown voltage.

  Each grid current detection unit 260B, 260Y, 260M, 260Y includes resistors R1-R4 connected in series with the constant voltage circuits 250B, 250Y, 250M, 250C. And the connection point with each constant voltage circuit 250B, 250Y, 250M, 250C among each resistance R1-R4 is connected to each A / D port A1-A4 provided in the control apparatus 110 via a signal line, respectively. Yes. From the above, a voltage proportional to the magnitude of the current (each grid current Ig) flowing through each connection line L1 to L4 is input to each A / D port A1 to A4. Therefore, by reading the input voltage level of each A / D port A1 to A4, the controller 110 can detect the magnitude of the grid current Ig of each charger 50B, 50Y, 50M, 50C. .

  Next, the development voltage application circuits 270B, 270Y, 270M, and 270C serve to apply the development voltages Vd1 to Vd4 to the development rollers 45B, 45Y, 45M, and 45C, and the development rollers 45B, 45Y, and 45M. , 45C are provided individually.

  The development voltage application circuits 270 </ b> B to 270 are commonly connected to the output line Lo of the charging voltage application circuit 200. Hereinafter, the development voltage application circuit 270B will be described as a representative circuit. The development voltage application circuit 270B includes a resistor Ra and a control transistor Tr2. One end of the resistor Ra is connected to the output line Lo of the charging voltage application circuit 200.

  The control transistor Tr is an NPN transistor, and has a collector connected to the other end of the resistor Ra and an emitter connected to the ground. Further, the base of the control transistor Tr is connected to the PWM port P1 of the control device 110 via a signal line. The signal line is provided with an integrating circuit including a capacitor C and a resistor R, and the PWM signal output from the PWM port P1 of the control device 110 is smoothed and applied to the base of the control transistor Tr2. ing.

  As described above, the developing voltage applied to the developing roller 45B can be controlled by adjusting the voltage applied to the base of the control transistor Tr2 by the PWM signal. The applied developing voltage is a voltage obtained by subtracting the voltage drop due to the resistor Ra from the output voltage Vo of the charging voltage applying circuit 200.

  The development voltage application circuits 270Y, 270M, and 270C are also composed of a resistor Ra and a control transistor Tr2 like the development voltage application circuit 270B, and the voltage applied to the base of the control transistor Tr2 is adjusted by a PWM signal. The developing voltage applied to each developing roller 45Y, 45M, 45C can be controlled.

  Further, as shown in FIG. 4, development voltage detection circuits 280B to 280C for detecting output voltages (development voltages) Vd1 to Vd4 are provided in the development voltage application circuits 270B to 270C, respectively. The development voltage detection circuits 280B to 280C are configured by resistors Rb and Rc connected in series, and are connected in parallel to the control transistor Tr of the development voltage application circuits 270B to 270C.

  At an intermediate connection point between the resistors Rb and Rc, a voltage is generated by dividing the output voltages Vd1 to Vd4 of each developing voltage applying circuit 270 according to the resistance ratio. And each A / D port A5-A8 of the control apparatus 110 is connected to the intermediate connection point of resistance Rb, Rc which comprises each developing voltage detection circuit 280B-280C through a signal line.

  Therefore, the output voltages Vd1 to Vd4 of the development voltage application circuits 270B to 270C can be detected from the voltage levels of the A / D ports A5 to A8.

  The control device 110 performs a function of controlling the grid current Ig flowing through the grid electrode 55 of the charger 50 and a function of controlling the developing voltages Vd1 to Vd4 applied to the developing rollers 45Y, 45M, and 45C. Five PWM ports P0 to P4 and nine A / D ports A0 to A8 are provided.

  The grid current Ig is controlled by outputting the PWM signal S0 from the PWM port P0 and adjusting the output voltage Vo of the charging voltage application circuit 200. The development voltages Vd1 to Vd4 are controlled by outputting PWM signals from the PWM ports P1 to P4 to the development voltage application circuits 270B to 270C.

  The control device 110 can be configured with a built-in CPU or an application specific integrated circuit (ASIC). The control device 110 includes a non-volatile storage unit (not shown), in which various data (for example, (a) to (d) below) are executed to execute a grid current control flow described below. Data).

(A) Reference value data of grid current Ig (250 μA)
(B) Data on the upper limit value of the grid current Ig (300 μA)
(C) Data of the lower limit value of the grid current Ig (200 μA)
(D) Data on the upper limit value of the output voltage Vo of the charging voltage application circuit 200 (8 kV)

  The grid current Ig is known to be approximately proportional to the discharge current flowing from the charger 50 to the photosensitive drum 41, and serves as an index for measuring the level of the discharge current flowing to the photosensitive drum 41. That is, if the grid current Ig is flowing at a reference value of 250 μA, the discharge current flowing through the photosensitive drum 41 becomes the reference level, and the charge amount of the photosensitive drum 41 becomes an appropriate level for maintaining the image quality.

  If the grid current Ig is in the range of 300 μA, which is the upper limit value, and 200 μA, which is the lower limit value, the magnitude of the discharge current flowing through the photosensitive drum 41 is generally within the allowable range. Note that 300 μA that is the upper limit value of the grid current Ig is an example of the “first threshold value” of the present invention, and 200 μA that is the lower limit value of the grid current Ig is an example of the “second threshold value” of the present invention.

  Next, the grid current control flow executed by the control device 110 will be described with reference to FIG. In the following description, each channel CH refers to each charger 50B, 50Y, 50M, 50C. In this example, the charger 50B is CH1, the charger 50Y is CH2, the charger 50M is CH3, and the charger. Let 50C be CH4.

  As shown in FIG. 6, when print data D is output from a host device such as a host computer, the print data D is received by the printer 1 through the interface IF. Then, a print processing start command is given from the main control unit 80 that controls and controls the entire printer 1 to the control device 110 of the high-voltage power supply device 100.

  As a result, the control device 110 starts the grid current control flow of FIG. 5 and applies a charging voltage to the wires 53 of the chargers 50B, 50Y, 50M, and 50C via the charging voltage application circuit 20. The initial target of the charging voltage is “6 kV”, for example. Then, following the application of the charging voltage, the control device 110 calculates and monitors the grid current Ig of each channel CH from the input voltage of each A / D port A1 to A4 (S10).

  Thereafter, the control device 110 detects the output voltage Vo of the charging voltage application circuit based on the input value of the A / D port A0 (voltage value detected by the voltage detection circuit 240), and sets the level of the output voltage Vo. judge. Specifically, it is determined whether the output voltage Vo is lower than the upper limit value of 8 kV. If the output voltage Vo is lower than the upper limit value of 8 kV, a YES determination is made, and then the process proceeds to S30. Moreover, when it is 8 kV or more, it becomes NO determination and it transfers to S90 after that.

  When it is determined that the output voltage Vo is smaller than 8 kV and the process proceeds to S30, the control device 110 compares the current value of the grid current Ig of each channel CH monitored in S10 to obtain the maximum grid current Ig. Then, the level of the maximum grid current Ig is determined. Specifically, it is determined whether the maximum grid current Ig is smaller than the upper limit of 300 μA. If the maximum grid current Ig is smaller than 300 μA, a YES determination is made, and then the process proceeds to S40. Moreover, when it is 300 μA or more, a NO determination is made, and thereafter, the process proceeds to S60. Here, the description is continued assuming that YES is determined.

  When it is determined that the maximum grid current Ig is smaller than 300 μA and the process proceeds to S40, the controller 110 causes the charging voltage application circuit so that the minimum grid current Ig of the grid current Ig of each channel CH becomes a constant current of 250 μA. The output voltage Vo of 200 is adjusted.

  In the example of FIG. 8, since the grid current Ig of the channel CH1 is minimum, the control device 110 monitors the input voltage of the A / D port A1 with respect to the channel CH1 and determines the output voltage Vo of the charging voltage application circuit 200. The grid current Ig of the channel CH1 is controlled to a constant current of 250 μA.

  Thereafter, the process proceeds to S50, and it is determined whether the application of the charging voltage is completed. If the application of the charging voltage has not ended, NO is determined in S50, the process proceeds to S10, and the same process as described above is executed in order from S10.

  Therefore, after the charging voltage application is started, NO determination is made in S20 and S30, that is, as long as the following two conditions are satisfied, the processing of S10 to S50 is repeated, and the grid current Ig of the channel CH1 becomes a constant current of 250 μA. The controlled state continues. As described above, in the present embodiment, the minimum grid current Ig is controlled to the reference value after the application of the charging voltage is started. Therefore, it is possible to keep the discharge amount of each charger 50 and the charge amount for each photosensitive drum 41 at an appropriate level or more, and it is possible to suppress deterioration in image quality due to insufficient charge amount.

Condition 1 is that the output voltage Vo of the charging voltage output circuit 200 is 8 kV or less.
Condition 2 is that the maximum grid current Ig is 300 μA or less, which is the upper limit value.

  When the application of the charging voltage is completed with the end of printing, a NO determination is made in S50. If NO is determined in S <b> 50, then, control device 110 stops the output of charging voltage output circuit 200. Thus, a series of processing ends.

  By the way, silica or dust adheres to the wire 53 of each charger 50 due to corona discharge accompanying the application of the charging voltage, so that the resistance value of the wire 53 of each charger 50 increases as the number of printed sheets increases. Become.

  Therefore, if the minimum grit current Ig is maintained at a constant current of 250 μA, the output voltage Vo of the charging voltage application circuit 200 tends to increase as the number of printed sheets increases (see FIG. 7), and the constant current increases to 250 μA. Except for the controlled channel (channel CH1 in the example of FIG. 8), the grid current Ig tends to increase (see FIG. 8). Note that the degree of increase in the grid current Ig differs between the channels because the amount of silica or dust attached to the wire 53 differs between the channels.

  In the grid current control flow of this embodiment, the grid current Ig of each channel is monitored in S10, and it is determined in S30 whether the maximum grid current Ig is smaller than 300 μA. During the charging voltage application, the maximum grid current Ig is determined. When Ig reaches the upper limit of 300 μA, a NO determination is made in S30.

  In this case, the grid current control flow deviates from the state in which the processes of S10 to S50 are repeated in order, and proceeds to S60 (S30: NO determination). In S60, the channel for constant current control is switched from the channel of the minimum grid current Ig to the channel of the maximum grid current Ig, and the control device 100 causes the maximum grid current Ig to become a constant current of 300 μA. The output voltage Vo of the charging voltage application circuit 200 is adjusted.

  In the example of FIG. 8, since the grid current Ig of the channel CH4 is maximum, the channel to be subjected to constant current control is switched from CH1 to CH4, and the control device 110 inputs the A / D port A4 to the channel CH4. The voltage is monitored, the output voltage Vo of the charging voltage application circuit 200 is adjusted, and the grid current Ig of the channel CH4 is controlled to a constant current of 300 μA.

  After the channel switching, the state in which constant current control is performed on the grid current Ig of the channel CH4 to 300 μA continues except when NO is determined in S20 and NO is determined in S70 (period 2 in FIG. 8). ).

  Therefore, since the grid current Ig can be suppressed to the upper limit value or less for all four channels, abnormal discharge of the charger 50, that is, large discharge current from the wire 53 of the charger 50 to the photosensitive drum 41 can be prevented. Therefore, it is possible to prevent deterioration of the photosensitive drum 41.

  Further, as shown in FIG. 9, the load of each charger 50 accompanying the increase in the number of printed sheets is proportional to the resistance value of the wire 53. In this embodiment, the constant current control channel is changed from a minimum grid current channel, that is, a channel having a large resistance value of the wire 53 and a large load of the charger 50 to a maximum grid current channel as the number of printed sheets increases. That is, the resistance value of the wire 53 is small and the load of the charger 50 is switched to a small channel.

  Therefore, as compared with the case where the channel is not switched, as shown in FIG. 7, it is possible to suppress the increase in the output voltage Vo of the charging voltage application circuit 200 accompanying the increase in the number of printed sheets. Therefore, it becomes difficult for the charger 50 to be abnormally discharged and the time until the output voltage Vo reaches the upper limit can be extended, so that the number of printed sheets can be increased.

  Next, in S70, the level of the minimum grid current Ig is determined. Specifically, it is determined whether the minimum grid current Ig is 200 μA or more which is the lower limit value. When the maximum grid current Ig is controlled to a constant current of 300 μA, if the minimum grid current Ig falls below the lower limit of 200 μA, a NO determination is made in the determination process of S70, and the process of S90 is executed. .

  In S90, the control device 110 executes a process for stopping the output of the charging voltage application circuit 200 and a process for displaying an error for a channel whose grid current Ig is less than 200 μA. In the example of FIG. 8, the channel CH <b> 1 is a target of error display, and for example, a message for urging the cleaning of the wire 53 for the charger 50 </ b> B of the channel 1 is displayed on a display unit outside the drawing.

  By performing such an error display, it is possible to avoid printing in a state where the grid current Ig is below the lower limit value, and thus it is possible to prevent deterioration in image quality.

  Further, as described above, since the resistance value of each wire 53 increases as the number of printed sheets increases, the output of the charging voltage application circuit 200 in both the period 1 in FIG. 8 and the period 2 in FIG. The voltage Vo, that is, the charging voltage of each charger 50 increases. In the present embodiment, the level of the output voltage Vo of the charging voltage application circuit 200 is determined in S20. If the output voltage Vo exceeds the upper limit value of 8 kV, NO is determined in S20, and the process proceeds to S80.

  After shifting to S80, the control device 110 monitors the input voltage of the A / D port A0, and controls the output voltage Vo of the charging voltage application circuit 200 to a constant voltage of 8 kV. Therefore, the charging voltage applied to each charger 50 can be suppressed to 8 kV or less, which is the upper limit value, and abnormal discharge of the charger 50 can be prevented.

  Note that, by the processing of S30 and S60 in FIG. 5 executed by the control device 110, the “grid current control unit” function of the present invention is “functions of the grid voltage application circuit by adjusting the output of the charging voltage application circuit. The maximum grid current having the maximum value among the grid currents flowing through the first current is controlled to a first threshold value equal to or greater than a reference value, that is, the maximum grid current is controlled to be 300 μA in the above example.

  Further, the processing of S30 and S40 in FIG. 5 executed by the control device 110 is a function of the “grid current control unit” of the present invention “of the grid current flowing through each grid electrode at the start of control”. , Constant current control is performed on the minimum grid current so that the minimum grid current with the minimum value is the reference value, that is, 250 μA in the above example.

  Further, by the processing of S70 and S90 in FIG. 5 executed by the control device 110, “the grid electrode during the constant current control of the maximum grid current” is a function of the “first notification unit” of the present invention. An error is reported for the scorotron charger in which the grid current flowing through the second threshold is smaller than the reference value, that is, 200 μA or less in the above example.

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, as in the first embodiment, after applying the charging voltage, the minimum grid current Ig is controlled to a constant current of 250 μA, and when the maximum grid current Ig reaches the upper limit as the number of printed sheets increases, Thereafter, the maximum grid current Ig is controlled to the upper limit of 300 μA. When the maximum grid current Ig is controlled at a constant current of 300 μA, the control is performed to lower the developing voltage Vd of the channel where the grid current Ig tends to decrease. 5), the processing from S100 to S140 shown in the one-dot chain line frame in FIG. 10 is added.

  The processing of S100 to S140 is a loop processing in which S110 to S130 are executed for each channel, that is, the number of channels is repeated four times (n = 1 to 4). Note that the symbol n shown in S100 and S140 in FIG. 10 represents the channel of the charger 50. Further, “n = 1, 4, 1” described in S100 means that the initial value is “1” and the final value is “4”, and the count is incremented by one.

  In S110, the control device 110 determines the magnitude of the grid current Ig for the selected channel n. Specifically, it is determined whether the grid current Ig is smaller than the reference value of 250 μA.

  If the grid current Ig is smaller than 250 μA, a YES determination is made and the process proceeds to S120. In S120, processing for lowering the target value of the development voltage Vd from the reference value of 400V is performed for the channel. Specifically, according to the following equation (1), the target value of the development voltage Vd is lowered following the decrease in the grid current Ig.

Vd = 400− (250−Ig) × α (1)
Ig indicates the magnitude of the grit current (μA).
α is an arbitrary constant.

  On the other hand, when the grid current Ig is 250 μA or more, NO is determined, and the process proceeds to S130. In S130, processing for setting the target value of the development voltage Vd to the reference value of 400V is performed for the channel.

  By performing these processes, for example, in the period 2 shown in FIG. 8, the two channels CH1 and CH2 whose grid current is less than 250 μA have the target value of the development voltage Vd of the grid current Ig as shown in FIG. It will be lowered by following the decrease of.

  As described above, in the second embodiment, since the channel whose grid current is less than 250 μA lowers the target value of the developing voltage Vd, the potential difference between the charging voltage on the photosensitive drum side and the developing voltage on the developing device side can be made constant. Therefore, it is possible to reliably attach the toner as the developer to the exposed portion of the photosensitive drum 41, so that it is possible to prevent so-called printing fog and the like, and it is possible to suppress deterioration in image quality.

  Also, as shown in FIG. 12, the process of S123 and the process of S125 are added to the grid current control flow of FIG. 10, and the target value of the development voltage Vd is below the lower limit value (for example, 300 V). In the case (S123: NO determination), it is preferable to display an error for the channel on the display unit (not shown) (S125). In this way, since the development voltage Vd does not fall below the lower limit value, the charge amount of the toner as the developer does not become insufficient, and deterioration in image quality can be further suppressed.

  It should be noted that the processing of S110 and S120 in FIG. 10 executed by the control device 110 is a function of the “developing voltage control unit” of the present invention, “during the constant current control of the maximum grid current, "The target value of the developing voltage is lowered" for the developing device that supplies the developer to the photoconductor facing the scorotron charger in which the flowing grid current is lower than the reference value, that is, 250 μA in the above example. .

  Further, as a result of the processing of S123 and S125 of FIG. 12 executed by the control device 110, the “developing device in which the applied developing voltage is lower than the lower limit value” is a function of the “second notification unit” of the present invention. "Inform the error about the scorotron charger that charges the photosensitive member supplied with the developer".

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) Embodiment 1 shows an example in which the upper limit value of the grid current Ig is applied to the “first threshold value” of the present invention, and an example in which the lower limit value of the grid current Ig is applied to the “second threshold value” of the present invention. Indicated. The “first threshold value” may be a numerical value that is equal to or greater than the reference value and corresponds to the upper limit value. For example, the first threshold value is set to a value that has a margin with respect to the upper limit value, that is, a numerical value that is slightly smaller than the upper limit value. Also good. Further, the second threshold value may be a numerical value that is equal to or lower than the reference value and corresponds to the lower limit value. Also good.

  (2) In the first embodiment, the minimum grid current Ig is controlled to a constant current of 250 μA until the maximum grid current Ig reaches 300 μA after the start of charging voltage application (period 1 in FIG. 8). In addition to the above, the control method for the period until the maximum grid current Ig reaches 300 μA immediately after the charging voltage is applied (period 1 in FIG. 8) is such that the total value of the grid current Ig of the four channels becomes 1 mA. Alternatively, constant current control may be performed.

  (3) In the second embodiment, the target value of the development voltage Vd is lowered for the channel where the grid current Ig is lower than the reference value of 250 μA, but the threshold value of the grid current that determines whether the development voltage Vd is lowered is the reference value. For example, the reference value of the development voltage may be lowered for a channel in which the grid current Ig is below the lower limit of 200 μA.

  (4) In the first and second embodiments, the configuration example of the printer 1 is an example in which one charger 50 is associated with one photosensitive drum 41 (in other words, one having the photosensitive drum 41 for each color). . In the present invention, in addition to the printer 1 having the configuration described in the first and second embodiments, for example, a plurality of chargers 310 and 320 are arranged corresponding to one photosensitive drum 300 as shown in FIG. The present invention can also be applied to a toner (a toner image of each color superimposed on the photosensitive drum 300 and then transferred to a sheet at once). In FIG. 13, reference numeral 315 denotes a process unit (developer) that forms a pair with the charger 310, and reference numeral 325 denotes a process unit that forms a pair with the charger 320.

  (5) In the first and second embodiments, the example in which the grid current detection circuits 260B, 260Y, 260M, and 260C are provided in each of the channels CH1 to CH4 is described. However, the grid current detection circuit is shared between the channels. Also good. In this case, the grid current may be detected by time division between the channels.

DESCRIPTION OF SYMBOLS 1 ... Printer 41B, 41Y, 41M, 41C (generally 41) ... Photosensitive drum (an example of "photoconductor" of the present invention)
50B, 50Y, 50M, 50C (generally 50) ... Scorotron charger 45B, 45Y, 45M, 45C (generally 45) ... developing roller (an example of the "developer" of the present invention)
53... Wire 55... Grid electrode 110... Control device ("Grid current control unit" of the present invention, "First notification unit" of the present invention, "Development voltage control unit" of the present invention, "Second notification unit of the present invention" Example)
200 ... charging voltage application circuit 260B, 260Y, 260M, 260C (collectively 260) ... grid current detection circuit (an example of the "current detection unit" of the present invention)
270B, 270Y, 270M, 270C (collectively 270)... Development voltage application circuit 280B, 280Y, 280M, 280C (collectively 280)... Development voltage detection circuit Ig.

Claims (7)

A photoreceptor,
A plurality of scorotron chargers for charging the photoreceptor;
Each of the scorotron chargers is commonly connected, and a charging voltage application circuit that applies a voltage to each of the scorotron chargers,
Each wire provided in each scorotron charger;
Each grid electrode provided in each of the scorotron chargers,
A current detector for detecting a grid current flowing to the each grid electrodes,
By adjusting the output of the charging voltage application circuit, constant current control is performed on the maximum grid current so that the maximum grid current having the maximum value among the grid currents flowing through the grid electrodes becomes a first threshold value equal to or greater than a reference value. A grid current control unit ,
The grid current controller is
At the start of control, constant current control is performed on the minimum grid current so that the minimum grid current of the grid current flowing through each grid electrode becomes the reference value.
An image forming apparatus that performs constant current control on the maximum grid current so that the maximum grid current becomes the first threshold after the maximum grid current reaches the first threshold . Each developer that supplies a developer of each color to each of the plurality of photoreceptors provided,
A developing voltage application circuit for applying a developing voltage to each of the developing devices;
A development voltage controller that controls the development voltage application circuit so that the development voltage of each of the developing devices becomes a target value;
The developing voltage controller is configured to supply the developer to the photoconductor facing the scorotron charger in which the grid current flowing through the grid electrode is lower than a reference value during constant current control of the maximum grid current. the image forming apparatus according to claim 1 for controlling lowering the target value of the developing voltage. A photoreceptor,
A plurality of scorotron chargers for charging the photoreceptor;
Each of the scorotron chargers is commonly connected, and a charging voltage application circuit that applies a voltage to each of the scorotron chargers,
Each wire provided in each scorotron charger;
Each grid electrode provided in each of the scorotron chargers,
A current detector for detecting a grid current flowing to the each grid electrodes,
By adjusting the output of the charging voltage application circuit, constant current control is performed on the maximum grid current so that the maximum grid current having the maximum value among the grid currents flowing through the grid electrodes becomes a first threshold value equal to or greater than a reference value. A grid current control unit ;
Each developer that supplies a developer of each color to each of the plurality of photoreceptors provided,
A developing voltage application circuit for applying a developing voltage to each of the developing devices;
A development voltage controller that controls the development voltage application circuit so that the development voltage of each of the developing devices becomes a target value;
The developing voltage controller is configured to supply the developer to the photoconductor facing the scorotron charger in which the grid current flowing through the grid electrode is lower than a reference value during constant current control of the maximum grid current. An image forming apparatus that performs control to lower the target value of the development voltage . Wherein the scorotron charger for the developing voltage to be applied is equal to or less than the lower limit value the developing unit charges the photosensitive member to be supplied with the developer, according to claim 2 or claim comprising a second notification unit for notifying an error Item 4. The image forming apparatus according to Item 3 . During the constant current control of the maximum grid current, the scorotron charger grid current flowing through the grid electrode is equal to or less than the reference value smaller than the second threshold, from claim 1, further comprising a first notification unit for notifying an error The image forming apparatus according to claim 4 .   A photoreceptor,
  A plurality of scorotron chargers for charging the photoreceptor;
  A charging voltage application circuit in which the scorotron chargers are connected in common;
  A wire provided in each of the scorotron chargers;
  A grid electrode provided in each of the scorotron chargers;
  A current detector for detecting a grid current flowing through each of the grid electrodes;
  A control unit,
  The controller is
  Voltage application processing for applying a voltage to the charging voltage application circuit;
  In the voltage application process, a determination process for determining whether or not a maximum grid current having a maximum current value among the grid currents is equal to or greater than a first threshold that is equal to or greater than a reference value;
  In the determination process, when it is determined that the maximum grid current is less than the first threshold value, the charging voltage application is performed so that the minimum grid current having the minimum current value among the grid currents becomes the reference value. The output voltage output from the circuit is adjusted, and when it is determined that the maximum grid current is not less than the first threshold, the output voltage is adjusted so that the value of the maximum grid current becomes the first threshold. And an adjustment process.   A plurality of photoconductors;
  A plurality of scorotron chargers for charging each of the photoreceptors;
  A charging voltage application circuit in which the scorotron chargers are connected in common;
  A wire provided in each of the scorotron chargers;
  A grid electrode provided in each of the scorotron chargers;
  A current detector for detecting a grid current flowing through each of the grid electrodes;
  A developing device provided corresponding to each of the photoconductors and supplying a developer to each of the photoconductors;
  A developing voltage application circuit to which each of the developing devices is connected;
  A control unit,
  The controller is
  Charging voltage application processing for applying a voltage to the charging voltage application circuit;
  In the charging voltage application process, an output voltage output from the charging voltage application circuit so that a value of the maximum grid current that maximizes the current value among the grid currents becomes a first threshold value that is equal to or greater than a reference value. Charging voltage adjustment processing to adjust,
  Development voltage application processing for applying a voltage to the development voltage application circuit;
  In the development voltage application process, a development voltage adjustment process for adjusting the output voltage output from the development voltage application circuit so that the development voltage applied to each of the developing devices becomes a target value.
  In the charging voltage adjustment processing, the scorotron charger provided with the grid electrode through which the minimum grid current flows when the value of the minimum grid current that minimizes the current value among the grid currents is less than the reference value. An image forming apparatus that executes a process of lowering a target value in the developing voltage adjustment process for the developing unit corresponding to the photosensitive member charged by the developing voltage as compared with a case where the minimum grid current is not less than the reference value.

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